1) Field of the Invention
The present invention relates to a technology for relaying process requests from clients to a server.
2) Description of the Related Art
In recent years, the Capacity on Demand (CoD) technology has become prevalent in client-server systems on the Internet. In the CoD technology, it is possible to change the number of servers depending on the volume of requests from clients.
The CoD technology was necessary and was put into practical use because of an increase in various services using the Internet as well as an increase in outsourcing businesses for routine tasks. The services using the Internet have a characteristic in that the volume of requests from the clients to the servers fluctuates in a wide range, sometimes of the order of several digits. However, very few service providers prepare or can prepare fixed facilities that are sufficient to cope with large volume of requests. On the other hand, a large-scale outsourcing business provider having an Internet Data Center (IDC) has become a host to a large number of customers providing such services.
In the CoD system, a server is provided to each customer, and servers are rented out from a shared server pool as required. That is, as shown in FIG. 8, when demands for a service from client 800 of an n-th customer is high, a CoD system managing apparatus 802a in a CoD system 802 allocates a required server in the shared server pool to the customer via a relay network 801. When the demands become low, the server that was allocated is deallocated. This can achieve stable service supply with the effective use of facilities and reduction in fixed cost.
Time is required to install an operating system (OS) and applications in a new server. If a large number of service requests arrive while a new server is being installed, overload is put on the system. This increases response time and reduces service level. Moreover, some requests are discarded, which leads to loss of business opportunities. Also, some of the discarded requests are retransmitted, thereby increasing loads. In CoD, the number of servers tends to be suppressed in normal times. Therefore, the CoD system is vulnerable to a sudden increase in volume of requests. Such a phenomenon tends to occur in the CoD system compared with the conventional case of operations of fixed facilities.
To get around the problems, in a conventional technology disclosed in Japanese Patent Laid-Open Publication No. 7-64892 (hereinafter, a first patent document), for example, requests are distributed according to loads on servers. This prevents overload due to unbalanced use of the servers and, furthermore, deterioration in response time for accepted requests. In another conventional technology disclosed in Japanese Patent Laid-Open Publication No. 2003-283556 (hereinafter, a second patent document), requests are selected depending on the priority, thereby preventing overload on the servers and deterioration in response time for the selected requests.
In the conventional general Hyper Text Transfer Protocol (HTTP: RFC1945, 2616) proxy, a request from a client is terminated at a Transmission Control Protocol (TCP) level. Therefore, at least discarding of a request due to a timeout at the TCP level can be prevented. In another conventional scheme, an arrangement is made for speedily installing an additional server. In still another conventional scheme, the number of servers required is estimated, and then the estimated number of servers is installed in advance so as to at least seemingly reduce an installation time.
However, in the conventional technology disclosed in the first patent document, no consideration is given to the case of queuing, in which unprocessable requests are retained for a long time due to a large number of demands from clients or a long server installation time. Therefore, some requests are inevitably discarded due to the occurrence of a timeout at an application level, as in the case of an HTTP service. This timeout time depends on the application or the user. For example, a request for viewing a WWW page is cancelled if the request cannot be processed within approximately eight seconds, and this is known as the “eight-second rule” (in this case, the timeout time is eight seconds). If the additional installing process takes only six seconds but processing requests retained during those six seconds further takes two or more seconds, the requests are also cancelled.
On the other hand, in the conventional technology disclosed in the second patent document, requests are not retained to begin with, but are selected or discarded. Therefore, only the selected requests are processed, and the rest are discarded. Also, the conventional HTTP proxy does not consider a timeout at an application level. Therefore, as with the conventional technology disclosed in the first patent document, when requests are retained for a long time, the occurrence of discard is inevitable. Even if the time required for the additional server installing process becomes shorter, fluctuations in the volume of requests during installation cannot be coped with. Moreover, even if the number of servers required is estimated and the required servers are installed in advance, an unexpected sudden increase in the volume of requests cannot be handled, to begin with. Therefore, in either case, discard will occur.
Discarding of requests can occur even if the conventional technologies are combined. At any rate, the occurrence of discard due to the occurrence of a timeout at an application level, which is not considered in the conventional technologies, is inevitable. As such, in the conventional CoD technology, discard of requests and deterioration in response time are inevitable when a sudden increase in the volume of requests occurs.